In wide-band code division multiple access (W-CDMA) systems, one of the most demanding tasks having a significant effect on the performance of the receiver is the channel estimation, in which the complex channel coefficients are estimated. The goal of channel estimation is to cancel the distortion caused to the transmitted signal by the radio channel such that as perfect a replica of the transmitted signal is retrieved as is possible.
This can be achieved by coherent demodulation in which the received signal is multiplied with the complex conjugated channel estimate. However, in multi-path fast fading conditions the coherent detection is difficult to achieve and a channel estimation method is required that works satisfactorily under the challenging fast fading circumstances.
The channel multi-path profile heavily affects the performance of the channel estimation due to the fact that the estimation must be done individually in each temporal rake finger of the rake receiver. The more multi-path components in the channel, the lower the signal-to-noise ratio (SNR) per rake finger, since the channel energy is distributed in the propagation paths.
In the forward link, i.e. the down-link, of a wide-band code division multiple access (WCDMA) system, a primary common pilot channel (P-CPICH) is broadcast over the entire cell or a sector. The P-CPICH is broadcast also in the case of a multi-beam arrangement (multiple beams per sector) and in user specific beam-forming. Therefore there always exists one such channel per sector regardless of the applied transmission scheme.
In systems utilizing adaptive antenna techniques, dedicated channels are usually transmitted through a narrow beam, which means that the P-CPICH and the down-link dedicated physical channels (DL-DPCH) usually experience different channel characteristics on transmission to a mobile station antenna.
In current known systems, the down-link dedicated physical control channel (DL-DPCCH) is used as the phase reference for the DL-DPCH in adaptive antenna systems because of the fact that the P-CPICH does not experience the same channel characteristics.
It is therefore an aim of the present invention to provide an improved technique for estimating parameters in the receiver of an adaptive antenna system.